The invention concerns a device for transmitting a rotational movement and an adjustment system for a motor vehicle seat comprising such a device.
Rotational transmission devices are known which comprise a flexible shaft and a sheath inside which the flexible shaft is housed rotationally. In particular, the flexible shaft can consist of a metal cable. In these transmission devices, in particular for the adjustment of a seat for a motor vehicle, the speeds of rotation of the flexible shaft in the sheath are higher than 2000 revolutions/minute, conventionally of the order of 3000 revolutions/minute. During rotation at such speeds, small-amplitude vibrations appear which propagate along the flexible shaft and cause noise.
Moreover, when a lubricating substance is provided inside the sheath, the rotation of the flexible shaft brings about an Archimedes screw effect which causes the displacement of the lubricating substance to the ends of the sheath. This therefore results in a loss of efficiency of the lubrication which is detrimental to the reliability of the transmission device.
The invention aims to overcome these drawbacks by proposing a device for transmitting a rotational movement whose flexible shaft has a substantially smooth surface. This is because the applicant noted that this characteristic made it possible on the one hand to significantly reduce the vibrations caused by the rotation of the flexible shaft and on the other hand to eliminate the Archimedes screw effect. To that end and according to a first aspect, the invention concerns a device for transmitting a rotational movement comprising a flexible shaft and a sheath inside which the flexible shaft is housed, said sheath being arranged in order to allow the rotation of said shaft inside said sheath. The outer surface of the flexible shaft is machined so as to have a substantially smooth surface finish.
According to a second aspect, the invention concerns an adjustment system for a motor vehicle seat, comprising at least one adjustment runner mounted on the structure of the vehicle and adjustable means for fixing the seat to said runner, said system also comprising a drive motor having at least one revolving output, said adjustment system also comprising such a transmission device, which is disposed between the output of said drive motor and said fixing means, so as to move said fixing means along said adjustment runner in response to a rotation of said output. The invention will be better understood from a reading of the following description, given with reference to the accompanying figures.